stream_settings: Remove pencil icon from 'General' tab in stream settings.

For user who is not an administrator.
Also implemented a banner that notifies the user if they can edit
the following settings (name/description and stream permission).
Also increased padding-top of stream header by 10px. This change is done
to increase vertical spacing between the banner
and the stream header.

Fixes #20001.

static/styles/subscriptions.css

@@ -857,6 +857,7 @@ h4.stream_setting_subsection_title {
 
     .stream-header {
         white-space: nowrap;
+        padding-top: 10px;
 
         .stream-name {
             display: inline-block;

static/templates/stream_settings/stream_settings.hbs

@@ -23,6 +23,9 @@
 
         <div class="general_settings stream_section">
             {{#with sub}}
+            <div class="stream-settings-tip-container">
+                {{> stream_settings_tip}}
+            </div>
             <div class="stream-header">
                 {{> stream_privacy_icon
                   invite_only=invite_only
@@ -31,7 +34,7 @@
                     <span class="sub-stream-name" title="{{name}}">{{name}}</span>
                 </div>
                 <div class="stream_change_property_info alert-notification"></div>
-                <div class="button-group">
+                <div class="button-group" {{#unless can_change_name_description}}style="display:none"{{/unless}}>
                     <button id="open_stream_info_modal" class="button rounded small btn-warning" title="{{t 'Change stream info' }}">
                         <i class="fa fa-pencil" aria-hidden="true"></i>
                     </button>

static/templates/stream_settings/stream_settings_tip.hbs

@@ -0,0 +1,7 @@
+{{#unless can_change_stream_permissions}}
+    {{#if can_change_name_description}}
+        <div class="tip">{{t "Only subscribers to this stream can edit stream permissions."}}</div>
+    {{else}}
+        <div class="tip">{{t "Only organization administrators can edit these settings."}}</div>
+    {{/if}}
+{{/unless}}